CVE-2026-1435: Graylog Authentication Bypass Vulnerability

CVE-2026-1435 Overview

CVE-2026-1435 is a session fixation vulnerability affecting the Graylog Web Interface version 2.2.3. The vulnerability stems from incorrect management of session invalidation after new logins. The application generates a new sessionId each time a user authenticates, but fails to invalidate previously issued session identifiers. These old session tokens remain valid even after multiple consecutive logins by the same user, creating a dangerous security gap.

As a result, a stolen or leaked sessionId can continue to be used to authenticate valid requests indefinitely. An attacker with access to the web service/API network (port 9000 or the HTTP/S endpoint of the server) can reuse an old session token to gain unauthorized access to the application, interact with the API/web interface, and compromise the integrity of affected accounts.

Critical Impact

Attackers can exploit leaked or stolen session tokens to maintain persistent unauthorized access to Graylog accounts, bypassing normal authentication controls and potentially compromising log management infrastructure.

Affected Products

• Graylog Web Interface version 2.2.3
• Graylog API endpoints accessible on port 9000
• Graylog HTTP/HTTPS web interface endpoints

Discovery Timeline

• 2026-02-18 - CVE-2026-1435 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-1435

Vulnerability Analysis

This vulnerability is classified under CWE-613 (Insufficient Session Expiration). The core issue lies in the session management implementation within the Graylog Web Interface. When a user successfully authenticates, the application correctly generates a new session identifier. However, the critical security failure occurs because the application does not implement proper session invalidation logic for previously issued tokens.

In a secure session management implementation, when a new session is created for a user, all previously issued sessions should be invalidated immediately. This prevents session token reuse attacks where an adversary who has obtained a valid session token (through network interception, XSS attacks, log file exposure, or other means) can use that token to impersonate the legitimate user.

The vulnerability allows network-accessible attackers to target the Graylog web service on port 9000 or any configured HTTP/HTTPS endpoint. Since Graylog is commonly used as a centralized log management solution, successful exploitation could grant attackers access to sensitive log data from across an organization's infrastructure.

Root Cause

The root cause of CVE-2026-1435 is the lack of session invalidation logic in the authentication handler. When processing login requests, the Graylog application creates new session identifiers without maintaining a record of previously issued sessions or implementing cleanup mechanisms. This design flaw means that session tokens effectively never expire based on subsequent authentication events, only through their natural timeout period (if configured).

The session management subsystem does not track active sessions per user account, making it impossible to invalidate old sessions when new authentication occurs. This architectural oversight creates a window where multiple valid sessions can exist simultaneously for the same user, with older sessions persisting indefinitely until they reach their timeout threshold.

Attack Vector

The attack vector for this vulnerability is network-based. An attacker must first obtain a valid session token through various means such as:

1. Network interception - Capturing session tokens transmitted over unencrypted connections or through man-in-the-middle attacks
2. Cross-site scripting (XSS) - If combined with other vulnerabilities, attackers could steal session cookies
3. Log file exposure - Session tokens may be inadvertently logged and exposed
4. Shoulder surfing or physical access - Obtaining tokens from browser developer tools or local storage

Once an attacker possesses a valid sessionId, they can make authenticated requests to the Graylog API and web interface. Even if the legitimate user logs out and logs back in (generating new sessions), the attacker's stolen token remains valid. The attacker can interact with all API endpoints and web functionality available to the compromised account, including viewing sensitive log data, modifying configurations, and potentially escalating privileges within the Graylog environment.

Detection Methods for CVE-2026-1435

Indicators of Compromise

• Multiple concurrent active sessions for the same user account from different IP addresses or user agents
• API or web requests authenticated with session tokens that were issued before the user's most recent login
• Unusual access patterns to Graylog endpoints from unexpected geographic locations or IP ranges
• Session activity continuing after a user has performed a logout action

Detection Strategies

• Implement session tracking to identify multiple simultaneous sessions per user and alert on anomalies
• Monitor Graylog access logs for requests from session tokens that predate the latest authentication event for each user
• Deploy network traffic analysis to detect session token reuse from different source IPs
• Configure SentinelOne Singularity to monitor for suspicious process behavior and network connections targeting Graylog endpoints

Monitoring Recommendations

• Enable detailed authentication logging in Graylog to capture all login events with timestamps and source information
• Set up alerts for session usage patterns that indicate potential token reuse or hijacking
• Monitor network traffic to port 9000 and Graylog HTTP/HTTPS endpoints for anomalous activity patterns
• Regularly audit active sessions and implement automated review processes for long-lived sessions

How to Mitigate CVE-2026-1435

Immediate Actions Required

• Upgrade Graylog to a patched version that properly invalidates sessions upon new authentication events
• Force logout all active sessions and require re-authentication for all users
• Review Graylog access logs for signs of unauthorized session reuse
• Implement network segmentation to limit access to Graylog management interfaces

Patch Information

Organizations should monitor the INCIBE Security Notice for official remediation guidance. Users of Graylog version 2.2.3 should upgrade to a patched version as soon as one becomes available. Contact Graylog support or check the official Graylog security advisories for the latest patch information.

Workarounds

• Implement IP-based access restrictions to limit Graylog web interface access to trusted networks only
• Configure shorter session timeout values to reduce the window of exposure for stolen tokens
• Enable HTTPS-only access and ensure secure cookie flags are set to prevent token interception
• Implement additional authentication layers such as VPN requirements or IP allowlisting for administrative access
• Monitor and manually terminate suspicious sessions through administrative tools while awaiting a patch

# Configuration example - Restrict Graylog access via firewall
# Allow access only from trusted management network
iptables -A INPUT -p tcp --dport 9000 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 9000 -j DROP

# Configure session timeout in Graylog server.conf (reduce from default)
# session_timeout = 1800